1. Field of the Invention
This invention relates to a method and apparatus for a printed wiring board for forming a protective water-soluble pre-flux film on the surface of a conductor pattern facing outwards.
2. Description of Related Art
In a printed wiring board, a pre-flux film is routinely formed on its conductor pattern following the formation of the conductor pattern and prior to ultimate inspection such as substrate appearance inspection. For forming this pre-flux film, a solvent type pre-flux or a water-soluble pre-flux is used.
Meanwhile, since the solvent type pre-flux, which enables quality stability for the pre-flux film due to its high adhesion to a conductor pattern to assure stabilized film forming and also due to its superior solder wettability, is prepared using a large quantity of the volatile organic compounds (VOCs), the tendency is to use the solvent type pre-flux only in a limited quantity in view of environmental protection.
On the other hand, in a water-soluble pre-flux, not employing the VOCs, sufficient quality stability cannot be realized as compared to the solvent type pre-flux. For example, the water-soluble pre-flux is inferior to the solvent type pre-flux in adhesion to the conductor pattern, such that stable pre-flux films cannot be formed. In addition, the water-soluble pre-flux liquid is inferior in solder wettability.